MTC

Medullary Thyroid Carcinoma (MTC) is a type of thyroid cancer that originates from the parafollicular cells (also known as C cells) of the thyroid gland. These cells are responsible for producing calcitonin, a hormone that helps regulate levels of calcium and phosphate in the blood. MTC can occur in both sporadic and hereditary forms, with the latter often associated with multiple endocrine neoplasia type 2 (MEN 2).

Etiology and Pathogenesis

MTC develops from the parafollicular C cells of the thyroid gland. The hereditary form of MTC is associated with mutations in the RET proto-oncogene. This genetic mutation can be inherited in an autosomal dominant manner, leading to the development of MTC as part of the MEN 2 syndrome. MEN 2 is further categorized into MEN 2A and MEN 2B, both of which include MTC as a primary component. Sporadic cases of MTC, which account for about 75% of all cases, do not have a known hereditary component but may also involve mutations in the RET gene or other genetic alterations.

Clinical Presentation

Patients with MTC may present with a thyroid nodule, neck pain, or symptoms related to compression of nearby structures in the neck. Additionally, because MTC cells produce calcitonin, patients may exhibit symptoms related to elevated levels of this hormone, such as diarrhea. In advanced cases, symptoms may include hoarseness, difficulty swallowing, or difficulty breathing.

Diagnosis

The diagnosis of MTC involves a combination of clinical evaluation, laboratory tests, imaging studies, and histopathological examination. Elevated levels of calcitonin in the blood are a key marker for MTC. Fine-needle aspiration (FNA) biopsy of the thyroid nodule, followed by cytological examination, can provide a definitive diagnosis. Genetic testing for RET mutations is recommended for patients diagnosed with MTC to identify those with hereditary forms of the disease.

Treatment

The primary treatment for MTC is surgical removal of the thyroid gland (total thyroidectomy) along with dissection of the lymph nodes in the neck. This approach aims to remove all cancerous tissue and reduce the risk of recurrence. For patients with advanced or metastatic MTC, targeted therapies that inhibit specific molecular pathways involved in the growth and spread of cancer cells may be used. These include tyrosine kinase inhibitors (TKIs) such as vandetanib and cabozantinib.

Prognosis

The prognosis for patients with MTC varies depending on the stage of the disease at diagnosis, with early-stage disease having a better outcome. The presence of distant metastases at diagnosis is associated with a poorer prognosis. Regular follow-up and monitoring of calcitonin and carcinoembryonic antigen (CEA) levels are important for detecting recurrence.

Epidemiology

MTC accounts for approximately 3-4% of all thyroid cancers. It can occur at any age but is most commonly diagnosed in adults.